Gas cap



FIG. 1 is a perspective view of a gas cap showing my new design;

FIG. 2 is a side elevational view thereof, it being understood that the broken line showing of the float mechanism for the gas gauge indicator is for illustrative purposes only and forms no part of the claimed design;

FIG. 3 is a top-plan view thereof; and

FIG. 4 is a bottom, plan view thereof. 

The ornamental design for a gas cap, as shown and described. 